I've just ordered from from Wakemakers (along with two 750 lb rear sacs.) How long does it take to fill the bow sac?

I don't know what your expectations are, but the integrated bow sac is not enough weight to offset 750s in the rear on a 205v hull. There is not nearly as much room under the seats in the bow of the 205v hull as there are in the x15. You might get 350-400lbs of weight up there with the ibs. I was always running another sac on in the walkway as well, so I got rid of mine and use the under seat area for storage and went with the 1000lb open bow triangle up there. You will probably only be able to fill the 750s a little over half full with just the ibs and kgb up front. If you don't have dedicated thru hulls for each pump, fill times will be brutal. It took me 25 minutes or so to fill before I added new thru hulls. Once you get it all setup, the wake is top notch.

I've just ordered from from Wakemakers (along with two 750 lb rear sacs.) How long does it take to fill the bow sac?

I had the timer for the KGB set to 3.5. I don't think that equates to minutes in any reality. I extended the time to 4.5 but it did not fill the bag completely but it was plenty full. I ended up toggling the switch while running a rider to get it completely full. So not knowing for sure I'd guess that the stock tank fills in under 5 minutes. Since the IBS is stuffed into the seat area, it is not going to be anywhere near the 650 lbs it could be if completely full uninhibited. I'd say no more than an additional 5 minutes. If I think of it I will time the next time out. Problem is that I aways get so focused in jumping into the water to start boarding...

I did not add it to make the wake bigger as much as to change the shape and the firmness of the wake. So now the wake is longer and narrower at a slower speed. I can now run the boat about 19 MPH and not have the wake spreading like the grand canyon.

I can't say what it would do for a surf wake as since we don't surf, I did not try running the boat at surf speed to see the wake. Even if I did I don't have any experience surfing off the boat so I would not be a good judge of the surf wake.

Previously, my boat would tend to run bow high as we normally have no one sitting up front so it really needed the weight. Now when I hit another boat's wake, my bow no longer jumps higher and slams down on the next wave but rather cuts through - another benefit.

I've fallen in love with my X-15 all over again. Maybe one of these days I'll get a ride in an X-25 or X-Star so that I can compare but maybe it is better that I don't.